As I was looking up at the sky tonight I realized something that was missing from SpaceEngine. In reality, dim stars appear neutral in color, because they are too dim for the human eye to perceive the color. Only in bright stars is the color really noticeable. I believe that this would be a good visual effect to implement in SpaceEngine. Currently in the program, a magnitude 5 star looks just as colorful as a magnitude -5 star. In reality, to the unaided eye the dim star would appear white/gray.

I think that a good feature to implement would be rendering star color saturation as a function of apparent magnitude (perhaps by an inverse-logarithmic or logistic curve?) If this could be made to be a toggle-able option that would be even better. This would give the sky a much more natural appearance when viewed in the engine.

Just a thought I had and felt like sharing. And I apologize if this has been mentioned before, I can't recall seeing it so I just went ahead and posted

I was trying to do these, but found the effect strange... First idea is to add a few lines in the final HDR shader, that will desaturate dim pixels, but this approach doesn't work well - desaturation affects even the dark rocks or evening sky on planets. The second attempt is to change star shader. This works, but with low desaturation threshold the effect is not noticeble, and with the entire galaxy it becomes black and white, which is noticeble especially with interstellar flight.

You may experiment with these parameters, maybe you will find some are good. This is the star_blur.glsl shader, red lines are the new code: